Template synthesis of the hierarchically structured MFI zeolite with nanosheet frameworks and tailored structure

Abstract

The hierarchical zeolite with MFI nanosheet frameworks was directly prepared under hydrothermal synthesis conditions using a series of tetra-headgroup rigid bolaform quaternary ammonium surfactants, where the bolaform surfactants act as dual structure-directing functions on two different length scales (micro- and mesoporous) simultaneously. The MFI zeolite nanosheets were characterized by a complementary combination of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption isotherms, Fourier transform infrared spectroscopy, ²⁷Al MAS NMR spectroscopy, thermogravimetric analysis and density functional theory calculations. The results suggested that the hydrophilic headgroups caused the aluminosilicate species to form MFI zeolite-like frameworks while the surfactant linkers with a rigid biphenol group directed MFI nanosheet layers into an ordered multilamellar mesostructure. The morphologies and textural properties of MFI zeolite nanosheets could be controlled with different surfactants. Since the synthesis of MFI zeolite nanosheets has great potential for industrial applications, our synthesis approach can be expected to be extended to other types of zeolites in order to improve their performance in targeted catalytic reactions.